Gibberellins are known as a plant growth regulator. Their plant growth regulating activities include, for example, seedless fruitage, maturation period acceleration and fruit enlargement of grape; fruit drop control for persimmon, navel orange and others; growth and development acceleration of Mituba (Cryptotaenia japonica MAKINO), spinach, Japanese butterbur and others; acceleration of growth and development of Udo salad plant (Aralia eordata THIMB) and others by breaking of dormancy; prevention of production of puffy tomato and others; fruit enlargement of cucumber and others; enhancement of number of set fruits of strawberries and others; and bloom acceleration of tulip, cyclamen and other flowers and ornamental plants.
Although gibberellin have various activities as mentioned above, its application is limited because it is expensive and must be applied to crops at a high concentration.
To obviate the difficulties of gibberellin, great progress is being made in development of synergists. For example, plant growth regulators having the following synergists have been proposed: parachlorophenoxyacetic acid (Japanese Examined Patent Publication (hereinafter abbreviated to "JP-B") S57-11281), cyclic-3',5'-adenylic acid (JP-B S57-15726), tryptophan (JP-B S58-27245), streptomycin (JP-B S60-39325), 6-benzyladenine (JP-B S61- 15044), choline (JP-B H5-78522), pyrazole compounds (Japanese Unexamined Patent Publication (hereinafter abbreviated to "JP-A") H4-199104) and abscisic acid (JP-A H5-139912). Most of the proposed plant growth regulators still have problems such that gibberellin must be applied at a high concentration, e.g., 100 ppm, for seedless fruitage and fruit enlargement of grapes, and the effect of plant growth regulation is not satisfactory.
Jasmonic acid esters represented by the general formula (1), below, are known compounds, which are described in WO94/18833. It is reported that the jasmonic acid esters have activities such as coloring improvement and sweetness enhancement of fruits of grape; growth and development acceleration of potatoes, rice, wheat and others; and fruit enlargement of strawberry, tomato and others. However, the activities of the jasmonic acid esters as observed when they are used alone, are not satisfactory for some crops.